Analysis on the Variation of Acidity and Chemical Compositions of Rainwater in Chengdu Urban Area

AbstrcatIn this paper the variation of acidity and chemical compositions of rainwater in Chengdu urban area is analyzed,based on the local acid rain monitoring data from 1995 to 2003.The results indicate that the acidity of rainwater shows some fluctuation and the frequency of acid rain fluctuates to a great extent.The annual average value of rain acidity and frequency are both good in 1999 and 2000,but get worse subsequently.The concentrations of ions in rainwater are high,which means the rainwater is contaminated seriously.In the research period,the value of C_(SO~(2-)_4)/C_(NO~-_3)in the rainwater is decreasing,which means SO~(2-)_4 and NO~-_3 play nearly the same roles in the acid rain formation.Nitrogen oxides are becoming the more important pollutants in acid rain.Grey correlation analysis indicates that the correlative sequence of the pH with alkali cations in rainwater is NH~+_4Ca~(2+)Mg~(2+)K~+Na~+ and that of (pH′) with acidic anions in rainwater is F~-Cl~-SO~(2-)_4NO~-_3.